The invention relates to a precision blanking press comprising a top, a base, and tie rods and columns that connect the top and base through non-positive connection, a knife-edged ring cylinder being disposed in the top, a knife-edged ring piston for moving knife-edged ring pins being guided in said cylinder, a main piston/ram disposed in the base, the piston/ram making a stroke movement and supporting a table top and having a counterstay cylinder chamber in which a counterstay piston is guided, a central adjusting mechanism disposed coaxial to the stroke axis and comprising an adjusting nut with internal threading and a knife-edged ring cylinder with external threading for adjusting the upper clearance relative to the main piston, and a hydraulic system for supplying the cylinder chambers disposed in the top and base with a fluid that is set to a predetermined pressure.
Press frames consisting of assembled components have existed for a long time.
DE 471 188 C2 discloses a press frame with stationary and rigidly connected beams, both ends of which are connected together by a cast iron frame connector piece.
DE 581 753 A discloses a press frame with assembled members and guiding tools, wherein the press table can move perpendicular to the press direction relative to the cross head, the cross head remaining fixed.
A dual-pedestal press for cutting or stamping out circuit boards from a belt of material is described in DE 22 58 655 C3, wherein the top, the pedestals and the table are connected together and secured by way of tie rods.
What all of these known press frames have in common is that the upper cross head or yoke is fixed and therefore the upper clearance cannot be adjusted, which makes these solutions unsuitable for precision blanking.
DE 1 279 622 A1 discloses a precision stamping press comprising a blanking piston, a pressing piston that presses the sheet material against the press table and a counterpressure piston that supports the part of the workpiece to be stamped out, wherein an adjusting spindle for adjusting a stop flange sits in the press head, the spindle limiting the upward stroke of the moving yoke. The lower stroke-limiting stopping of the moving yoke is adjusted by rotating threaded cylinders that fit one inside the other. The finely-threaded adjustment step is done using a hand wheel by way of a bottom worm gear on a gearwheel that is directly attached to the external threaded cylinder, whereas an electric motor is provided for rapid adjustments, the motor driving the screw by way of two bevel gears.
This known blanking head height-adjustment system does not provide sufficient adjustment and exactitude relative to the height position of the head due to the manual operation of the system. Another disadvantage is that repeatability of adjustment is low, with the quality of the precision cut parts suffering as a result.
Another disadvantage is that during blanking, spindle rotation, due to the naturally present axial play between the cylinders, cannot be completely eliminated.
Other known solutions use shaft key arrangements to adjust the distance between an upper die fastened to the ram of a press, the upper die cooperating with a lower die fastened to the press table (DE 2 039 644 A1), or hydraulically-actuated cylinders (DE 198 22 436 A1). However, these known solutions are unsuitable for precision blanking presses due to the interactions of the blanking piston, the knife-edged ring piston and the knife-edged ring pins.
According to EP 2 258 495 B1, a hydraulic precision blanking head for a mechanical press is known which is held on a top piece placed on a machine frame of the press above a ram that supports a table top and makes a stroke movement, the blanking head being in axial alignment with the stroke axis of the ram. A tubular part of a flange is used in the top piece, the collar of the tubular part being fastened non-rotationally by way of threaded connections on the side of the top piece facing the ram. The main cylinder is pushed concentrically into the tubular part, a knife-edged ring piston and a contact piston being disposed in the main cylinder, wherein the main cylinder is sealed shut pressure-tight by a cover or by a holding block. The main cylinder is connected to a hydraulic system that supplies the main cylinder with a fluid that is adjusted to a predetermined pressure.
The position of the hydraulic head relative to the ram is adjusted using an adjustment mechanism comprised of an adjusting nut that is provided with an inner adjustment threading and an outer adjustment threading disposed on the top of the main cylinder, the positioning being effected by way of a sprocket that is non-positively fastened at an end of the adjusting nut and disposed perpendicular relative to the stroke axis, a hydraulic motor and drive shaft held at the top, a drive chain looped around the drive shaft of the motor and the sprocket, and a brake that can be applied to the drive shaft, wherein the adjustment threading is connected to a channel for feeding the hydraulic system fluid, which has been regulated to an adjustable pressure, for the purposes of eliminating and releasing the axial play of the threads.
This known precision blanking head requires a series of open chambers to be pressurized with hydraulic medium and/or lubricant, which reduces the stiffness of the design and thereby the high force transmission needed for precision blanking. Also, this top piece is complicated due to the multitude of parts, and the adjusting nut is only secured by the sprocket at the top, such that adjustment forces are introduced essentially without any axial securing being done.